1. Field of the Invention
The present invention relates to improved etching chambers and, more particularly, to improved reactive ion etching chambers as employed in the fabrication of integrated circuits.
2. Description of the Problem and Prior Art
One of the difficulties encountered with prior art reactive ion etching (RIE) systems resides in the fact that, typically, they do not etch uniformly over the entire area of the target. The lack of uniformity and etch rate is caused, at least in part, by defects and deficiencies in the chamber design. The problem of lack of uniformity in system etching performance is compounded when larger and larger cathode targets are employed to increase throughput in etching semiconductor wafers. In this regard, it is evident that as larger target cathodes are employed, larger reaction chambers are required, and larger reaction chambers introduce a variety of conditions which affect etch rate uniformity within the chamber. However, it is known that commercially competive systems must exhibit a high throughput characteristic, and high throughput necessitates the use of large batch etching.
The various prior art chamber and target cathode configurations have done little to alleviate the design defects which give rise to conditions which foster nonuniform etching within the chamber. For example, the so-called "top hat" cathode configuration operates to drive the cathode as the active electrode and utilizes a design which may result in lack of uniformity in the electric field above the cathode, particularly at its edges. Such a design is described in copending application Ser. No. 185,831 by Hendricks et al., filed Ser. 10, 1980, and assigned to the assignee of the present invention. Large area cathodes and chamber volumes, in general, tend to introduce non-uniformity in the electric field and, thus, the etching rate. In this regard, large chambers also generate excess plasma which acts to dissipate some of the energy introduced into the chamber, thus diluting the energy available for the etching process. In general terms, the lack of uniformity in the electric field is due not only to irregularities and discontinuities within the internal chamber surface area, but also due to the lack of a symmetrical characteristic to the chamber and cathode.
In addition to the lack of uniformity in etching, design characteristics may also introduce other problems. For example, sputtering and incident contamination may also result from faulty design characteristics. In this regard, the typical so-called "Tee" design, as commercially available in the market place, has a structural arrangement which permits plasma to be generated in the space below the electrode. The plasma below the cathode electrode excessively heats the electrode and causes a sputtering thereof of contaminants which find their way into the product being etched.
The various RIE tools heretofore known in the prior art all exhibit design defects which act to limit their ability to provide batch processing with a uniformity in etching in a contamination free environment. In accordance with the principles of the present invention, it has been found that improved RIE operations may be achieved by utilizing a chamber design which is cylindrical and physically symmetrical with respect to the cathode plate. In addition, all required apertures within the chamber are arranged to have opening dimensions less than the thickness of the "dark" space for the particular tool, whereby tool field uniformity is improved and points of field concentration are avoided. Thus, "hot spots" in the plasma leading to localized higher etch rates, as caused, for example, by the irregularities and discontinuities of windows, apertures, diagnostic ports and pumping ports are avoided by minimizing the size of the openings and the critical placement of same within the RIE chamber. Particularly good results are achieved by designing the cathode plate so as to extend to the chamber sidewalls with the isolation separation between sidewalls and plate being less than the thickness of the system "dark" space.
It is, therefore, an object of the present invention to provide an improved RIE system.
It is a further object of the present invention to provide an improved RIE chamber and cathode design.
It is yet a further object of the present invention to provide an RIE chamber which will permit batch processing of product.
It is yet still a further object of the present invention to provide an RIE system which will permit the batch processing of product with uniform etching.
It is yet still a further object of the present invention to provide an RIE chamber which will permit the batch processing of product with uniform etching in a contaminant free chamber.
The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention, as illustrated in the accompanying drawings.